Performances of local chitosan and its nanocomposite 5%Bentonite/Chitosan in the removal of chromium ions (Cr(VI)) from wastewater.

The present work focuses on the study of the application of abundant and less expensive materials such as chitosan (CS) and bentonite/chitosan nanobiocomposite (nano 5%Bt/CS) in the removal of hexavalent chromium. The adsorption behavior of the prepared materials (CS and nano 5%Bt/CS) was tested for the removal of chromium (VI) ions in a synthetic solution and wastewater from a tanning industry. Spectroscopic analysis like techniques FTIR, XRD and SEM/EDX have been used to characterise the adsorbents before and after their contact with chromium ions. The experimental data indicate that the adsorption of chromium proceeds kinetically according to a pseudo-second order model on both adsorbents and the apparent activation energy (Ea) have been measured to be 4.11kJmol-1 and 15.98kJmol-1 for chitosan and nano 5%Bt/CS, respectively. It was found that the non-linear modelling of experimental isotherms was well adapted to the Langmuir and Redlich-Peterson models. Thermodynamic parameters (i.e., change in the free energy (ΔG°), the enthalpy (ΔH°), and the entropy (ΔS°)) have been also, evaluated and the results revealed that the removal of chromium ions on both solids was done via physical adsorption. The adsorption test on a real rejection of the tanning industry shows that the CS and nano 5%Bt/CS can substitute other more expensive adsorbents.

Adsorption studies of Cu(II) onto biopolymer chitosan and its nanocomposite 5%bentonite/chitosan.

Chitosan (CS) and nanocomposite 5%bentonite/chitosan (5%Bt/CS) prepared from the natural biopolymer CS were tested to remove Cu(II) ions using a batch adsorption experiment at various temperatures (25, 35 and 45°C). X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis/differential thermal analysis (TGA/DTA) were used in CS and the nanocomposite characterisation. This confirmed the exfoliation of bentonite (Bt) to form the nanocomposite. The adsorption kinetics of copper on both solids was found to follow a pseudo-second-order law at each studied temperature. The Cu(II) adsorption capacity increased as the temperature increased from 25 to 45°C for nanocomposite adsorbent but slightly increased for CS. The data were confronted to the nonlinear Langmuir, Freundlich and Redlich-Peterson models. It was found that the experimental data fitted very well the Langmuir isotherm over the whole temperature and concentration ranges. The maximum monolayer adsorption capacity for the Cu(II) was 404-422 mg/g for CS and 282-337 mg/g for 5%Bt/CS at 25-45°C. The thermodynamic study showed that the adsorption process was spontaneous and endothermic. The complexation of Cu(II) with NH(2) and C = O groups as active sites was found to be the main mechanism in the adsorption processes.